To the doctors at the Shifa hospital in Gaza City it was another body on a chaotically busy day. By early Saturday afternoon the morgue was already overflowing so they laid out the corpse of 20-year-old Ali Abu Rabia on the floor outside. One of the hospital staff pulled out a mobile phone from his pocket, scrolled through the numbers, and called the young man's father.

"I was at work. Someone from the hospital called and said they had found my son," said Marwan Abu Rabia, 44, a plumber. "I went straight to the hospital and found him lying on the floor outside the morgue. There were too many bodies. It looked like a massacre."

The hospital was so crowded staff held back relatives outside the building and turned away the lightly injured. They struggled to treat the seriously hurt, some of whom lay on beds in the corridors because of the congested wards.

Palestinian officials said the death toll from Saturday's air strikes was at least 280, with another 600 people injured. Most are thought to be police or security officials, but among the casualties were many civilians.

Several more Palestinians were killed and injured yesterday, although the Israeli air strikes were less extensive. One Israeli civilian was killed on Saturday by a rocket fired by Palestinian militants from Gaza.

Ali Abu Rabia was a student at a UN vocational college for Palestinian refugees in the Rimal district of Gaza City. He sat an exam on Saturday morning, his father said, and after the first Israeli air strikes decided to go home. He was standing in the street with others when an Israeli missile struck, at around 1.30pm. Reportedly it had been aimed at a policeman seen nearby with a walkie-talkie.

"It was a place full of students. It was not a military base. But in spite of this they still attacked, all because of one policeman," said Ali's father as he greeted mourners at a funeral tent at his home yesterday "Our situation is very bad and the cause is Israel. The response has to be very tough." He said he doubted there would be a peace agreement with Israel in the coming years. "I don't believe they want an independent Palestinian state," he said.

In that single air strike seven students were killed and another 20 were injured. The Guardian has learned of several other civilians who were killed and injured in the same strike on Saturday.

Chris Gunness, a spokesman for the UN Relief and Works Agency, which supports Palestinian refugees and feeds 750,000 Gazans, called for an inquiry into the attack. "Grave question marks hang over this killing ... There must be an investigation and the facts must get out. There must be accountability."

Another funeral tent was put up at a family home a few hundred metres away. Nehru Rayes, 47, was presiding over a funeral for his two sons Hisham, 25, a carpenter, and Alam, 18, who had been at school, and their cousin Abdullah, 21, who ran an internet cafe. All three were killed in the street, in the same air strike.

Rayes, a petrol station attendant, learned from the Shifa hospital that all three were dead, and that two other relatives had been injured. Representatives from the rival Palestinian factions Fatah and Hamas had come to his house offering, as usual, to help with the costs of the funeral. He refused them both. "We've become like the homeless, begging for electricity, cooking gas and food," he said.

He spoke of the "corruption" of the previous Fatah governments and then said of the Hamas leaders: "They have everything they want: cooking gas, generators, and they can move whenever they want. But the Palestinian people are suffering."

Like many in Gaza yesterday, he spoke angrily of a desire for revenge against Israel. "When they fight face to face with armed groups that's OK, but when they attack civilians it's not acceptable," he said. "We need to go back to a ceasefire, eventually, but it has to mean all the crossings are open again and life returning to normal."

As he spoke another relative, Morad Rayes, 46, interrupted: "The disagreement between Hamas and Fatah gave the Israelis the reason to attack Gaza. All the ordinary people are suffering in this bad economic situation. It's just those belonging to the factions who benefit. We are facing a tough enemy. We have to be united."

Inside the Shifa hospital yesterday there were still relatives pouring through the corridors, looking for the injured. Most of the wounded spoke bitterly of their experience.

Mohammad Jahjouh, 21, lay on a hospital bed with cuts to his legs and side. He was injured late on Saturday night when an Israeli missile struck a mosque close to the hospital. "I thought I was dead but then I started to move my hands and legs and I screamed for help," he said. He was carried into the hospital. "It's unjust, unfair and aggression. After this huge number of casualties it would be a sign of weakness for us to ask for a ceasefire."

Gaza's streets were largely empty yesterday, with most shops closed and queues only at local bakers where people were stocking up with supplies.

Mowaffaq Alami, 35, was close to the main security headquarters, the Suraya, in Gaza on Saturday when it was attacked in the first round of Israeli air strikes at around 11am. "People were walking through the streets just like a normal day, children coming home from school. Suddenly, without any warning, the bombing started. We didn't even see the jets in the sky. That's why so many people were killed," he said. He said the first round of attacks was over within a few minutes but left dozens dead.

Alami lives in an apartment nearby and runs the Gaza office of One Voice, an initiative that works to support a two-state solution to the Israeli-Palestinian conflict. "People are following the news, wondering what's coming next," he said. "People are very worried there may be an invasion. We used to plan our lives day by day. Now, it's hour by hour."